Structure of the obese protein
leptin-E100.

Leptin is a hormone made by cells in fat tissue that reduces hunger. That helps the energy balance in the body.

Leptin is opposed by the actions of the hormone ghrelin, the "hunger hormone". Both hormones act on receptors in the hypothalamus. They adjust appetite to get energy homeostasis.

In obesity, a decreased sensitivity to leptin comes up. This leads to a feeling of hunger, despite high energy stores.